The present invention relates to a form and seal unit for a machine for packaging pourable food products.
Machines for packaging pourable food products, such as fruit juice, wine, tomato sauce, pasteurized or long-storage (UHT) milk, etc., are known in which the packages are formed from a continuous tube of packaging material defined by a longitudinally sealed strip.
The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal material, such as polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of barrier material, defined for example by an aluminium film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material defining the inner face of the package eventually contacting the food product.
In the manufacture of aseptic packages, the strip of packaging material is unwound off a reel and fed through an aseptic chamber in which it is sterilized, e.g. by applying a sterilizing agent such as hydrogen peroxide, which is subsequently evaporated by heating, and/or by subjecting the packaging material to radiation of appropriate wavelength and intensity; and the sterilized strip is folded into a cylinder and sealed longitudinally to form, in known manner, a continuous, longitudinally sealed, vertical tube. That is, the tube of packaging material forms an extension of the aseptic chamber, and is filled continuously with the pourable food product and then fed to a form and (transverse) seal unit for producing the individual packages, and in which the tube is gripped between pairs of jaws to seal the tube transversely into pillow packs, which are then separated by cutting the sealing portions between the packs.
More specifically, the portion of the tube pressed between the jaws is simultaneously sealed transversely by heating means, e.g. induction or ultrasonic, carried by the jaws. Once the sealing operation is completed, a cutter is activated to cut the tube of packaging material along the center of the sealed portion and so cut a pillow pack off the bottom end of the tube. Since the bottom end is sealed transversely, the jaws, on reaching the bottom dead center position, can be opened to prevent interfering with the top part of the tube. At the same time, the other pair of jaws, operated in exactly the same way, moves down from the top dead center position to repeat the above gripping/forming, sealing and cutting operations.
The pillow packs are then fed to a final folding station where they are folded mechanically to form the finished packages.
Known units also comprise, for each pair of jaws, two forming flaps, which are positioned facing each other, are hinged to the jaws, and are movable between a withdrawn or open position, and a forward or closed position in which they meet, in the closed position of the jaws, to define a cavity defining the shape and volume of the package to be formed in between.
In one known solution, the closing movement of the forming flaps is governed by cams fixed to the structure of the machine, and which interact with respective rollers carried by the tabs.
Machines of the above type have proved highly successful commercially and extremely reliable, to the extent of requiring very little maintenance even after many years"" service.
On the other hand, such machines have several drawbacks, mainly in terms of flexibility.
Though adaptable to produce packages of different volumes, machines of the above type call for major alterations, which consist in changing the forming flaps on the jaws, and all the parts, even static (such as the cams), governing the closing movement of the tabs, as well as adjusting the new system. Besides the cost of manufacturing the replacement components, such alterations therefore involve a good deal of downtime.
In the technical sector considered, a demand therefore exists for a form and seal unit enabling fast changeover in the size of the packages, with no major alterations to the machine.
According to the present invention, therefore, there is provided a form and seal unit as claimed in claim 1.
According to the present invention, therefore, there is provided a form and seal unit for producing aseptic sealed packages, containing a pourable food product, from a tube of packaging material filled with the food product and fed along a vertical path. The unit comprises a fixed structure and two forming assemblies interacting alternately and cyclically with the tube of packaging material, and having respective slides movable vertically in reciprocating manner with respect to the structure. Respective pairs of jaws are carried by the slides, and have sealing members movable between an open position and a closed position in which the sealing members cooperate with the tube of packaging material; and including respective pairs of forming flaps. Each forming flap is carried by a respective one of the jaws and have a half-shell forming portion; the forming flaps of each forming assembly being movable between a withdrawn position spaced from said tube, and a forward position in which said respective half-shell forming portions enclose said tube. In the closed position, the respective jaws form a cavity of predetermined volume. The unit includes cams for controlling the closing movement of the forming flaps from the withdrawn position to the forward position, and includes cams carried by the forming flaps and interacting, during the movement of said jaws, with rollers fixed to the structure.